Apparatus for generating data for determining a property of a gemstone and methods and computer programs for determining a property of a gemstone

ABSTRACT

An apparatus for generating data for use in determining a property of a gemstone, such as a cut diamond, the apparatus comprising:  
     a support structure for supporting a gemstone placed at an observation position, the support structure being arranged such that, if the gemstone has an axis of symmetry, the gemstone is supportable such that the axis of symmetry is parallel to an axis X passing through the observation position;  
     illumination means arranged to illuminate a gemstone so placed with a spatially varied light pattern;  
     rotation means arranged to cause relative rotation between the light pattern and the support structure generally about the axis X;  
     a camera arranged to capture, at each of a plurality of rotational positions, an image of light returned by the gemstone and to output said images as image data.

FIELD

[0001] The present invention relates to electronic apparatus forgenerating data for determining properties of gemstones, such as cutdiamonds, as well as methods of and computer programs for determiningproperties of gemstones using the generated data. In particular, but notexclusively, it relates to electronic apparatus for generating data fordetermining properties as well as methods of and computer programs fordetermining properties of gemstones in which a plurality of images ofthe gemstone are captured for analysis under different lightingconditions.

BACKGROUND

[0002] The beauty of a gemstone, such as a cut diamond, derives from itslight handling ability. What attracts the eye is the “game of light”played by a well-cut diamond as incident light is reflected andrefracted off its many facets. Diamonds and other gemstones may be cutaccording to many different standardised cut patterns such as thestandard round brilliant cut, oval, pear, marquise, radiant, princess,heart, emerald cut etc. The most popular cut is the standard roundbrilliant (SRB) cut as shown in FIG. 1. Diamond cutting and polishing isa highly skilled art and a well-cut diamond, having superior opticalperformance, will command a significant price premium over a poorly cutdiamond having inferior optical performance.

[0003] When showing a cut diamond to an untrained observer, onefrequently refers to the four C's of a gemstone, being its carat weight,its clarity, its cut and its colour. Carat weight, clarity and colourcan be relatively easily measured objectively and are thereforegenerally useful. Cut may also be specified or measured in terms of thegeometry of the various facets. However, what really matters is thelight handling ability of the gemstone and reference is often made tomore subjective parameters of a cut diamond, such as its brilliance (theintensity of light returned), scintillation (fast and local fluctuationsin the light returned as the diamond moves relative to the lightingconditions), fire (the dispersion of white light into spectral colours)and symmetry (the symmetry of light patterns such as the so-called“hearts and arrows”). It can be difficult, particularly for an untrainedobserver, to make a personal appraisal of these subjective parameters.It can also be difficult to compare the light handling abilities of twodiamonds with the same carat weight, clarity and colour, and thereforeto appreciate why one is more valuable than the other.

[0004] It is recognised that properties such as brilliance, fire andsymmetry should be derived, whether by experimental observation ortheoretical computer modelling, under a variety of lighting conditions.Moreover, with the property of scintillation it is clearly essential toobserve or model the diamond under a variety of lighting conditions.Electronic apparatus for capturing images of gemstones under varyinglighting conditions for analysis are known.

[0005] International Patent Publication number WO 96/23207 describes adevice which captures colour images of a gemstone placed in an analysischamber and illuminated by a uniform annular light which may be movedalong an axis such that the gemstone may be illuminated from a pluralityof different angles. The device performs a spectral analysis of thecaptured images using a tuneable optical band pass filter to determinethe colour of the gemstone. Digital images of the gemstone may also bestored, displayed or transmitted over a data network.

[0006] The website (www.gemex.com) of GemEx Systems, Inc, a US company,describes a device called the BrillianceScope Analyser which isdescribed as an imaging spectrophotometer. Colour images of a diamondare captured in a controlled lighting environment consisting of sixlighting angles, five of which provide reflected light and one of whichprovides diffuse lighting. These images may then be analysed to generatea report on the diamond. The BrillianceScope Analyser device operates onthe same principle as the device described in International PatentPublication number WO 96/23207 referred to above, in that the gemstoneis placed in an analysis chamber and illuminated by a uniform annularlight which may be moved along an axis such that the gemstone isilluminated from different angles. The images may be analysed by acomputer, and the properties of “white light”, “coloured light” and“scintillation” for a diamond are determined and displayed on three linechart scales from ‘low’, to ‘medium’ to ‘high’. Captured images may alsobe shown in a repeating sequence in one display area, giving the effectof light movement.

[0007] International Patent Publication number WO 99/61890 describes asystem for the standardised grading of gemstones. A gemstone is subjectto a plurality of incident light sources and images are captured foranalysis. Images of the gemstone, such as a SRB cut diamond, may becaptured from various viewpoints such as from the pavilion, from thecrown and side-on. The gemstone is supported by a rotatable platformwhich is rotated when images are being captured from a side-on viewpointto obtain profile and colour images from a variety of rotationalpositions and to detect internal flaws and inclusions. When capturingimages from above and below the gemstone, the platform is moved along anaxis from a level position to a down and an up position respectively.The fixed focal length camera is also moved along an axis to focus onthe gemstone when the platform is moved between the up, down and levelpositions. A captured image may be analysed by a processor to obtaincolour measurements and measures of the brilliance and scintillation ofthe gemstone.

[0008] One object of the present invention is to provide an electronicapparatus, method and computer program for generating data for improveddetermination of properties of a gemstone, such as brilliance,scintillation, fire and symmetry.

[0009] Another object of the present invention is to provide anelectronic apparatus for generating data for determining properties ofgemstones which is more compact, lightweight, mechanically simpler, andtherefore less expensive to manufacture, than conventional apparatus,making it more suitable for use in retail premises, such as jewellersshops.

[0010] Another object of the present invention is to provide anelectronic apparatus, method and computer program enabling a observer tomore easily compare two diamonds and their properties, in particular theproperties of brilliance, scintillation, fire and symmetry.

[0011] Another object of the present invention is to provide anelectronic apparatus, method and computer program for generating datafor determining properties of a cut gemstone which is adapted to andtakes into account attributes of the shape and/or symmetry of the cutpattern of a particular gemstone.

[0012] Another object of the present invention is to provide anelectronic apparatus, method and computer program for generating datafor determining properties of a gemstone in which the gemstone isilluminated under more realistic lighting conditions.

[0013] Another object of the present invention is to provide anelectronic apparatus, method and computer program for measuring thesymmetry of a gemstone in terms of the light returned.

SUMMARY OF THE PRESENT INVENTION

[0014] According to a first aspect of the present invention there isprovided an apparatus for generating data for use in determining aproperty of a gemstone, such as a cut diamond, the apparatus comprising:

[0015] a support structure for supporting a gemstone placed at anobservation position, the support structure being arranged such that, ifthe gemstone has an axis of symmetry, the gemstone is supportable suchthat the axis of symmetry is parallel to an axis X passing through theobservation position;

[0016] illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern;

[0017] rotation means arranged to cause relative rotation between thelight pattern and the support structure generally about the axis X; and

[0018] a camera arranged to capture, at each of a plurality ofrotational positions, an image of light returned by the gemstone and tooutput said images as image data.

[0019] By rotating the spatially varied light pattern relative to thesupported gemstone about the axis of symmetry of the gemstone, andcapturing images at a plurality of rotational positions, the apparatusis particularly adapted to determining properties of cut gemstoneshaving radially symmetric cut patterns, such as SRB cut diamonds. Theintensity levels, and colour component proportions, of light returned atany particular spatial region of the gemstone are sensitive torotational movement. Thus, brilliance, symmetry, fire and scintillationare more easily, accurately and objectively measurable. Furthermore,unlike the prior art referred to above, which are generally mechanicallycomplex, and have laterally moving parts for varying the lightingconditions, the apparatus of the present invention advantageouslyemploys rotationally moving parts for varying the lighting conditions,thus enabling the apparatus to be manufactured in a relatively compactand lightweight form, and relatively inexpensively.

[0020] In preferred embodiments, the light pattern comprises at leastone relatively light region and at least one relatively dark region, theregions being arranged radially about the axis X. Preferably, the lightpattern is generally symmetrical about the axis X. Also preferably, thelight pattern has an n-fold symmetry, such as a 4-fold or 8-foldsymmetry, where n is a whole number multiple or factor of s, astandardised gemstone cut having an s-fold symmetry.

[0021] Thus, the light pattern illuminating the gemstone, correspondsclosely to particular gemstone cut patterns, such as the SRB cut, whichhave a particular shape and a particular arrangement of radiallysymmetric facets, resulting in the images captured having greatercontrast levels between different spatial regions of the gemstone andthe intensity levels, and colour component proportions, of lightreturned at any particular spatial region of the gemstone having greatersensitivity to rotational movement. Thus, brilliance, symmetry, fire andscintillation are more easily, accurately and objectively measurable.Furthermore, the light pattern illuminating the gemstone is a morerealistic simulation of the light that would illuminate a gemstone innormal, everyday use—for instance when mounted in an item of jewellerysuch as a ring. Light is not normally uniform around the axis ofsymmetry of the diamond and incident only at a narrow range of anglesoff the axis, as in prior art approaches. Instead, light is normallyincident at a wide range of angles off the axis of symmetry of thediamond and not uniform around the axis as in the present invention.

[0022] In other preferred embodiments, the illumination means comprisesa reflector having a concave surface arranged to reflect light generallytowards the gemstone, the concave surface having at least one relativelyreflective region and at least one relatively unreflective region,thereby creating said light pattern. Preferably, the reflector isrotatably mounted in said apparatus generally about the axis X, therebyenabling relative rotation between the light pattern and the supportstructure generally about the axis X. Alternatively, the platform isrotatably mounted in said apparatus generally about the axis X, therebyenabling relative rotation between the light pattern and the supportstructure generally about the axis X. Preferably, the illumination meanscomprises an annular light source arranged to emit light towards theconcave surface and an annular baffle arranged to prevent direct lightreaching the gemstone.

[0023] Thus, the apparatus requires only a single stationary lightsource and a rotatable reflector or rotatable support structure toenable rotation of the light pattern relative to the supported gemstone,resulting in improved mechanical simplicity, as well as reduced size,weight and cost of manufacture.

[0024] In a further preferred embodiment, the apparatus comprises a dataprocessing device arranged to determine a property of the gemstone bycomparing, using image data corresponding to one or more of saidelectronic images, the intensity of light at a first and a second imageportion, each portion comprising one or more pixels, said first andsecond image portions corresponding to a first and a second region ofthe gemstone respectively, said first and second regions being relatedto each other in accordance with a symmetrical property of astandardised gemstone cut.

[0025] Thus, an objective measurement of the symmetry of a gemstone isenabled in terms of the actual light returned from the gemstone and theexpected symmetry of the gemstone, such as the 8-fold symmetry of an SRBcut diamond, rather than based on potentially unrealistic or inaccuratemodels of the geometry of the cut pattern of the gemstone.

[0026] In a further preferred embodiment, the apparatus comprises a dataprocessing device arranged to determine a property of the gemstone bycomparing, using image data corresponding to two of said electronicimages, the intensity of light at one or more pixels of a first image,captured at a first rotational position, with the intensity of light atone or more pixels of a second image, captured at a second rotationalposition different to said first rotational position, said one or morepixels of the first image corresponding to the same region or regions ofthe gemstone as said one or more pixels of the second image.

[0027] Thus, an improved objective measurement of scintillation isenabled, using data from a plurality of images obtained at differentrotational positions of the spatially varied light pattern. With cutgemstones having cut patterns with many radial facets, such as the SRBcut with 32 differently angled facets in the crown and 24 differentlyangled facets in the pavilion, scintillation may be measured moreaccurately as, in particular, the intensity levels of returned lighthave a greater sensitivity to rotational movement of the light patternrelative to the gemstone than to variation of the angle of incidence ofthe light source.

[0028] In a further preferred embodiment, the apparatus comprises a dataprocessing device arranged to determine a property of the gemstone bycomparing, using image data corresponding to two of said electronicimages, the proportions of colour components at one or more pixels of afirst image, captured at a first rotational position, with theproportions of colour components at one or more pixels of a secondimage, captured at a second rotational position different to said firstrotational position, said one or more pixels of the first imagecorresponding to the same region or regions of the gemstone as said oneor more pixels of the second image.

[0029] Thus, an improved objective measurement of fire is enabled, usingdata from a plurality of images obtained at different rotationalpositions of the spatially varied light pattern. With cut gemstoneshaving cut patterns with many radial facets, such as the SRB cut with 32differently angled facets in the crown and 24 differently angled facetsin the pavilion, fire may be measured more accurately as, in particular,the proportions of colour components of returned light have a greatersensitivity to rotational movement of the light pattern relative to thegemstone than to variation of the angle of incidence of the lightsource.

[0030] According to a second aspect of the present invention there isprovided a method of generating data for use in determining a propertyof a gemstone, such as a cut diamond, the method comprising:

[0031] supporting a gemstone at an observation position, such that, ifthe gemstone has an axis of symmetry, the gemstone is supportable suchthat the axis of symmetry is parallel to an axis X passing through theobservation position;

[0032] illuminating the gemstone with a spatially varied light pattern;

[0033] causing relative rotation between the light pattern and thegemstone generally about the axis X;

[0034] capturing, at each of a plurality of rotational positions, animage of light returned by the gemstone.

[0035] According to a third aspect of the present invention, there isprovided a method of determining a property of a gemstone by comparing,using image data corresponding to one or more electronic images of thegemstone, the intensity of light at a first and a second image portion,each portion comprising one or more pixels, said first and second imageportions corresponding to a first and a second region of the gemstonerespectively, said first and second regions being related to each otherin accordance with a symmetrical property of a standardised gemstonecut.

[0036] According to a fourth aspect of the present invention, there isprovided a method of determining a property of a gemstone by comparing,using image data corresponding to two or more electronic images of thegemstone captured under different lighting conditions, the intensity oflight at one or more pixels of a first image, captured under a firstlighting condition, with the intensity of light at one or more pixels ofa second image, captured under second different lighting condition, saidone or more pixels of the first image corresponding to the same regionor regions of the gemstone as said one or more pixels of the secondimage.

[0037] According to a fifth aspect of the present invention, there isprovided a method of determining a property of the gemstone bycomparing, using image data corresponding to two or more electronicimages of the gemstone captured under different lighting conditions, theproportions of colour components at one or more pixels of a first image,captured under a first lighting condition, with the proportions ofcolour components at one or more pixels of a second image, capturedunder a second different lighting condition, said one or more pixels ofthe first image corresponding to the same region or regions of thegemstone as said one or more pixels of the second image.

[0038] According to a sixth aspect of the present invention, there isprovided a computer-implemented method of comparing properties ofgemstones, such as cut diamonds, the method comprising:

[0039] receiving first image data in respect of a first gemstone andsecond image data in respect of a second gemstone, said first and secondimage data each comprising one or more images of said first and secondgemstones, respectively;

[0040] determining a property of each of said first and second gemstonesin dependence on said first and second image data respectively; and

[0041] simultaneously displaying one or more images of each of saidfirst and second gemstones together with a representation of thedetermined property for each of said first and second gemstones.

[0042] Thus, an observer, such as a potential purchaser untrained inevaluating properties of gemstones, may compare two gemstones by meansof a side by side graphical representation on a computer screen and bymeans of objectively determined properties, such as brilliance,scintillation, fire and symmetry.

[0043] According to a seventh aspect of the present invention, there isprovided a apparatus for comparing properties of gemstones, such as cutdiamonds, the apparatus comprising:

[0044] a support structure for supporting a gemstone placed at anobservation position;

[0045] illumination means arranged to illuminate a gemstone so placed;

[0046] a camera arranged to capture an image of light returned by agemstone and to output said images as image data; and

[0047] a data processing device arranged to:

[0048] receive first image data in respect of a first gemstone andsecond image data in respect of a second gemstone, said first and secondimage data each comprising one or more images of said first and secondgemstones, respectively;

[0049] determine a property of each of said first and second gemstonesin dependence on said first and second image data respectively; and

[0050] simultaneously display one or more images of each of said firstand second gemstones together with a representation of the determinedproperty for each of said first and second gemstones.

[0051] Due to the compact, lightweight and inexpensive format of theapparatus, the gemstone analysis and comparison may be performed inretail premises, such as in a jeweller shop, with the potentialpurchaser present.

[0052] According to a eighth aspect of the present invention, there isprovided an apparatus for generating data for use in determining aproperty of a gemstone, such as a cut diamond, the apparatus comprising:

[0053] a support structure for supporting a gemstone placed at anobservation position, the support structure being arranged such that, ifthe gemstone has an axis of symmetry, the gemstone is supportable suchthat the axis of symmetry is parallel to an axis X passing through theobservation position;

[0054] illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern;

[0055] rotation means arranged to cause relative rotation between thelight pattern and the support structure;

[0056] a camera arranged to capture, at each of a plurality ofrotational positions, an image of light returned by the gemstonegenerally along the axis X and to output said images as image data.

[0057] According to a ninth aspect of the present invention, there isprovided a apparatus for generating data for use in determining aproperty of a gemstone, such as a cut diamond, the apparatus comprising:

[0058] a support structure for supporting a gemstone placed at anobservation position;

[0059] illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern;

[0060] rotation means arranged to cause relative rotation between thelight pattern and the support structure generally about an axis Xpassing through the observation position;

[0061] a camera arranged to capture, at each of a plurality ofrotational positions, an electronic image of light returned by thegemstone generally along the axis X and to output said images as imagedata.

[0062] According to a tenth aspect of the present invention, there isprovided a apparatus for generating data for use in determining aproperty of a gemstone, such as a cut diamond, the apparatus comprising:

[0063] a support structure for supporting a gemstone placed at anobservation position;

[0064] illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern;

[0065] rotation means arranged to cause relative rotation between thelight pattern and the support structure generally about an axis Xpassing through the observation position;

[0066] a camera arranged to capture, at each of a plurality ofrotational positions, an electronic image of light returned by thegemstone and to output said images as image data.

[0067] Further aspects and features of the present invention are set outin the appended claims, and further advantages will be apparent from thefollowing description, given by way of example only, in which:

BRIEF DESCRIPTION OF DIAGRAMS

[0068]FIGS. 1a and 1 b show a standard round brilliant cut diamond froman elevated side-on perspective and from a top-down view, respectively;

[0069]FIG. 2 shows an apparatus for generating data for determining aproperty of a gemstone according to the present invention;

[0070]FIGS. 3a and 3 b show the concave surface 26 of the apparatus ofFIG. 2 having exemplary patterns of relatively reflective and relativelyunreflective regions;

[0071]FIG. 4 shows a screen shot of the main screen of a computerprogram for analysing images of gemstones according to the presentinvention;

[0072]FIG. 5 shows four images of a cut diamond captured a differentrotational positions.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0073]FIGS. 1a and 1 b show the geometry of a standard round brilliant(SRB) diamond. FIG. 1a shows the diamond from an elevated side-on view.The top most domed-shaped portion of the diamond is known as the crown10. The bottom most conical portion of the diamond is known as thepavilion 12. At the top of crown 10 at the centre is a relatively largefacet known as the table 14. The bottom most point of the pavilion 12 isknown as the culet 16. FIG. 1b shows the SRB diamond from a top-downview, looking along an axis from the centre of the table 14 through theculet 16. There are 32 facets on the crown 10 of the SRB cut diamond,not including table 14, and 24 facets on the pavilion, not includingculet 16. It can be seen that the radial facets of the SRB cut diamond(56 in total plus one for the table and one for the culet) have an8-fold symmetry about an axis passing though the centre of table 14 andculet 16.

[0074]FIG. 2 shows a cross-sectional view of an apparatus for generatingdata for determining properties of a gemstone according to the presentinvention. A gemstone such as a cut diamond 20 is placed on a platform(not shown) at an observation position with its table-side face-down.The platform is an optically clear glass plane of regular thicknessarranged within the apparatus so that it is substantially horizontalwhen the apparatus is in a horizontal position. The platform may becoated with an anti-reflection coating and provided with a small ringunderneath to reduce glare. The apparatus is mounted in a housing (notshown) which prevents external light from reaching the diamond 20 anddust from entering the mechanical and optical components. The housinghas a access lid above the platform for placing and removing a gemstoneto be measured. The inner surface of the housing and lid above theregion of the platform is coated with an unreflective material so thatsubstantially no light is reflected back from the lid or housing towardsthe gemstone or platform.

[0075] Diamond 20 is illuminated by an annular light 24, such as afluorescent tube light or halogen light. Annular light 24 emits visiblelight of frequency comparable to daylight. A suitable annular light is aStocker and Yale microscope illuminator with a White 5500HC fluorescentring light having a colour temperature of 5500° K, which produces alight close to Northern daylight. Light from annular light 24 isprevented from directly reaching diamond 20 by an annular baffle 28disposed between the annular light 24 and the diamond 20. However, lightfrom annular light 24 is reflected off a concave surface 26 of areflector and generally towards diamond 20. The reflector may be asemi-spherical shell centred on the observation position with the innersurface of the shell being concave surface 26.

[0076] The reflector is mounted within the apparatus such that concavesurface 26 is rotatable about an axis 22 perpendicular to the platformand such that when diamond 20 is placed at the observation position, thecentre of its table and its culet lie approximately along axis 22.Annular light 24 and annular baffle 28 are stationary and disposedwithin the apparatus such that they are also perpendicular to andcentred around axis 22. A stepper motor (not shown) is provided forrotating the reflector, and concave surface 26, about axis 22.

[0077] A viewing hole 34 is present at the bottom of the reflector andconcave surface 26 where they meet axis 22. A digital camera having acharged couple device (CCD) sensor array, or a complementary metal-oxidesemiconductor (CMOS) sensor array, and capable of being controlled by apersonal computer (PC), is positioned within the apparatus such that itcan capture an image of diamond 20 along the axis 22. The camera is acolour camera having a fixed focal length, at least a 640×480resolution, a memory capable of storing at least one image, and a datacommunication interface, compatible with standards such as the UniversalSerial Bus (USB), RS 422 parallel port or IEEE 1394 “Firewire”standards, for transferring captured image data to an external device,such as a PC. The camera is focussed on the plane made by the topmostsurface of the platform on which diamond 20 is placed, and has asuitable depth of field such that sharp images may be captured ofgemstones of the largest size reasonably expected to be measured. Anoptically clear mirror 32 may be disposed within the apparatus so thatthe light path between camera 30 and diamond 20 need not be a straightline, thereby enabling a more compact format of apparatus. A suitabledigital CCD camera is a Unibrain Fire-i Digital CCD colour camera with aresolution of 640×480 or a Unibrain Fire-i400 Industrial version with asimilar resolution. A suitable digital CMOS camera is a Silicon ImagingMegaCamera SI-3170 RGB camera, with a maximum resolution of 2056×1560, a12-bit per pixel colour depth.

[0078] The apparatus, including the light 24, baffle 28, reflector withconcave surface 26, mirror 34, stepper motor, camera 30, and housing,but not including the PC, is compact in size (having dimensions ofapproximately 123 mm×112 mm×200 mm) and lightweight (approximately 3.875kg).

[0079] Camera 30 and the stepper motor are connected to and controllableby a PC 36. PC 36 may be a portable PC such as a laptop or notebookcomputer having an Intel Pentium III central processing unit (CPU), 128megabytes of memory, an LCD panel screen and a 10 gigabyte hard discdrive. PC 36 has a USB port, a parallel port and/or IEEE 1394 “Firewire”port for connecting to the camera and stepper motor, and a 2D videoprocessing chipset for frame grabbing. By means of a suitable computerprogram, as will be described in greater detail below, PC 36 controlsthe stepper motor to rotate concave surface 26 through a series ofpredetermined rotational positions. PC 36 also controls camera 30 tocapture images of diamond 20 at a suitable frame rate such that an imagemay me stored at each of the series of rotational positions of concavesurface 26. The image data captured by camera 30 is transferred to PC 36in the form of a bitmap or other suitable image file format for displayand analysis. The image data is transmitted as a continual live imagefeed to the PC 36.

[0080] The range of angles through which concave surface 26 is rotatedis dependent upon the symmetry of the light pattern reflecting offconcave surface 26. With a light pattern having a 4-fold symmetry, forexample, images are captured at a plurality of rotational positions asconcave surface 26 is rotated through a 90° range. Within the range, thenumber of images captured at different rotational positions for use inanalysis depends on the cut pattern of the gemstone being measured, orthe cut pattern of the most faceted gemstone likely to be measured.Generally, the number of images should be at least 4 times the number ofdifferently angled facets within the range through which concave surface26 is rotated. Thus, with a SRB cut diamond having 32 differently angledfacets in its crown and pavilion and thus 8 differently angled facetswithin a 90° range, at least 32 images (4*8) should be captured over the90° range. For general purpose, it has been found that a generallysuitable number of images to be captured is 45. Thus, over a 90° range,concave surface 26 is rotated in steps of 2°. It will be understood thathigher or lower numbers of images may be used as appropriate to the cutpattern of the gemstone, the accuracy of measurement required and theprocessing capabilities of the PC 36.

[0081]FIGS. 3a and 3 b show the concave surface 26 looking down from thediamond observation position along axis 22. Concave surface 26 has aplurality of relatively reflective regions 40 and relativelyunreflective regions 42 formed by coating the surface with relativelyreflective and relatively unreflective materials. FIG. 3a shows oneconfiguration of regions 40 and 42 in which concave surface 26 isdivided into eight equal radial sectors, arranged around the axis 22,which are alternately relatively reflective and relatively unreflective.FIG. 3b shows a further configuration of regions 40, 42 in which concavesurface 26 is divided into 16 equal sectors, arranged around the axis22, of alternate relatively reflective and relatively unreflectiveregions. It can be seen that the configuration of regions 40 and 42 ofFIG. 3a each have a four-fold symmetry about the axis 22 whereas theconfiguration of regions 40 and 42 of FIG. 3b each have an eight-foldsymmetry about axis 22. Other configurations of relatively reflectiveregions 40 and relatively unreflective regions 42 are envisaged withinthe scope of the present invention. Concave surface 26 may have a mattfinish.

[0082] During operation of the apparatus, it can be seen that the lightreflecting off concave surface 26 towards the diamond 20 at itsobservation position has a spatially varied pattern determined by theconfiguration of relatively reflective regions 40 and relativelyunreflective regions 42. In particular, the light pattern, as observedin the plane of the platform, will have a series of radial peaks andtroughs of light intensity corresponding to the configuration. Thus,with the configuration of FIG. 3a, the light pattern will have fourradial peak lines and four radial trough lines. Similarly, with theconfiguration of FIG. 3b, the light pattern will have 8 radial peaks and8 radial troughs. Furthermore, with diamond 20 table-side down on theplatform, the light will be reflected generally towards the crown at abroad range of angles of incidence relative to axis 22, as predominantlyoccurs when diamonds are mounted in rings and other jewellery foreveryday use.

[0083] The selection of a particular configuration of relativelyreflective regions 40 and relatively unreflective regions 42 isdependent upon the standardised cut of diamond 20. For example, adiamond of SRB cut has an eight-fold symmetry as described above, and asuitable configuration of regions 40 and 42 would be that as shown inFIG. 3a, in which there are eight sectors in total—four relativelyreflective sectors 40 and four relatively unreflective sectors 42. Thus,the light pattern reflecting of concave surface 26, having four radialpeaks and four radial troughs corresponds to the symmetry of the cutgemstone in that adjacent symmetrical sectors of the gemstone (of 45°)will receive corresponding radial light pattern sectors (of 45°) havingadjacent peaks and troughs. As concave surface 26 is rotated through90°, the intensity of light as observed at any radial line in the planeof the platform and about axis X, will go through a single completecycle having a single peak and a single trough.

[0084] PC 36 may run a standard operating system, such as MicrosoftWindows XP or the like. PC 36 also executes a computer program arrangedto control the stepper motor to rotate concave surface 26 and to controlcamera 30 to capture and transfer to PC 36 images of diamond 20 at eachof the predetermined rotational positions, for example, 45 images takenat rotational steps of 2° over a total range of 90°. Control over thestepper motor is achieved by using a conventional stepper motor controlcircuit, such as a Motorola MC 3479 stepper motor controller, tointerface between PC 36 and the stepper motor and executingcorresponding program elements on PC 36 for sending digital controlsignals to the stepper motor control circuit. Control over camera 30 isachieved using the camera's inbuilt control interface and executingcorresponding program elements on PC 36 for sending digital controlsignals to camera 30.

[0085] The program elements controlling the stepper motor and camera 30are themselves under control of a main computer program executing on PC36 and able to receive user instructions via a user interface to causethe series of images of diamond 20 to be captured and transferred fromcamera 30 to the PC 36, to analyse the images using various algorithmsto obtain measurements of optical properties of diamond 20 and todisplay the images on the screen of the PC 36. FIG. 4 shows a screenshot of the main menu screen of the computer program. On the right andleft sides of the main menu screen are images of two different diamonds,captured in separate scanning operations. An image of a diamond on theright or left sides of the main menu screen may be a “live” image ascurrently being captured by camera 30 or a “video” image as previouslycaptured during a scanning operation and stored in the hard disk driveof the PC 36. A “video” image may be presented as a moving image withthe diamond being shown in consecutive rotational positions. Beneatheach image are measurements of the diamond's optical properties ofbrilliance, scintillation and symmetry represented in numerical format(0 to 100) and as a graphical bar chart. Algorithms for calculatingthese measurements will be described below. An average of the threemeasurements is also provided labelled “Total” giving an overall measureof the three optical properties. Thus, a user, such as prospective buyercan compare two diamonds, scanned in two separate scanning operations,side by side both visually on PC 36 screen and in terms of objectivemeasurements of the optical properties of brilliance, scintillation andsymmetry.

[0086] Five push buttons are presented in the centre of the screen foruser control of the computer program and apparatus. A “Scan” push buttonis provided for causing the computer program to initialise a scan ofdiamond 20. Initially, diamond 20 is manually placed table-side down onthe platform and centred on axis 22. This may be assisted by observingthe live image of the diamond displayed on PC 36 screen. Then, thestepper motor is controlled to rotate concave surface 26 to a “home”position and then to each of the series of rotational positions, forexample 45 positions over a 90° range in steps of 2°. Frames grabbedfrom camera 30 at each of these positions are stored in the hard discdrive of PC 36 for later display and analysis. The results of analysis,ie the measurements of brilliance, scintillation and symmetry, are thendisplayed.

[0087] A “Calibrate” push button is provided for calibrating the systemto compensate for variations in the intensity of the light produced byannular light 24. Calibration is performed by rotating concave surface26 to a predetermined position, and placing an angled mirror on theplatform in a predetermined position, such that camera 30 views a knownportion of concave surface 26. The known portion concave surface 26 maycomprise relatively reflective and relatively unreflective regions 40,42. An image captured by camera 30 of the known portion of concavesurface 26 is then analysed by integrating the light intensity levelsover all pixels to determine a total light intensity level received. Thetotal light intensity level is then used to adjusts gain and brightnesssettings of camera 30. Calibration is preferably performed at regularintervals and immediately prior to scanning.

[0088] A “Camera” push button is provided for altering the defaultsettings of the camera. A “Tools” push button is provided for selectingvarious options for the computer program such as a) whether the computerprogram determines the circumference of a gemstone automatically ormanually; b) if manually, for providing user interface means to indicateit; c) how fast concave surface 26 is rotated; and d) the frequency withwhich stored frames, captured at different rotational positions, aresequentially displayed on the screen of PC 36. An “Exit” push button isalso provided for closing exiting the computer program.

[0089] To calculate the three measures of brilliance, scintillation andsymmetry, from the stored images, three separate algorithms are used. Ineach case, the main computer program first analyses the images todetermine the circumference of diamond 20 and its centre point. Thecircumference is determined by first summing the light intensity levelsat each pixel over all the images at different rotational positions, forexample 45 images, to obtain a composite image. Then, all pixels of thecomposite image having a light intensity level above a predeterminedthreshold (representing a light level slightly above the level of theblack background) are selected. Then the smallest circle containing allthe selected pixels is determined and this is defined as thecircumference of diamond 20.

[0090] Once the circumference and centre of diamond 20 is determined,the three algorithms are executed to calculate measurements of the threeoptical properties only in respect of pixels contained within thecircumference and excluding pixels outside the circumference. FIG. 5shows four images of a cut diamond captured at different rotationalpositions together with a circle defining the circumference of thediamond and a cross marking the centre point. It can be seen thatvarious geometrical patterns of light and dark regions are formed and,in different rotational positions, the regions appear either relativelylight or relatively dark.

[0091] To calculate a measure of the brilliance of diamond 20, theaverage light intensity level (ie brightness) is determined over eachpixel within the circumference of diamond 20 and for each of the storedimages at different rotational positions. Thus, if there are n pixels inthe circumference of diamond 20, and 45 images at different rotationalpositions, the light intensity level is averaged over 45*n pixels intotal. This results in an average light intensity level for diamond 20over all images at different rotational positions, which provides anobjective measure of the brilliance of diamond 20.

[0092] To calculate a measure of the scintillation of diamond 20, thedifference in light intensity levels (ie brightness) between a pixelfrom a first image (captured at a first rotational position) and itscorresponding pixel (at the same coordinate position) from a secondimage (captured at a second rotational position, one rotational stepafter the first rotational position) is determined. This is repeated forall pixels within the circumference of diamond 20 in the first andsecond images, and for all pairs of first and second images captured atrotational positions which are one rotational step apart. Thus, if thereare n pixels in the circumference of diamond 20, and 45 images atdifferent rotational positions, 44*n differences are calculated. Thenumber of times the absolute difference in light intensity levels isgreater than a predetermined threshold is counted for all pixels in thecircumference and for all pairs of images which are one rotational stepapart. The ratio of this number over the total number of pixel pairs,44*n, gives an objective measure of the scintillation of diamond 20.

[0093] To calculate a measure of the symmetry of diamond 20, for thecomposite image, composed of the stored images at each of the differentrotational positions, pixels within the circumference of diamond 20 aredivided into 8 approximately equal radial sectors about the centre ofdiamond 20. The number of sectors is chosen to correspond to the 8-foldsymmetry of the SRB cut pattern. Thus, if there are n pixels within thecircumference of diamond 20 in an image, each sector has approximatelyn/8 pixels. Then, the difference in light intensity levels (iebrightness) between each pixel in each of the 8 sectors of an image andits corresponding pixels (ie the corresponding pixels as rotated byi×45°, where i=1 to 7) in the seven other sectors of the same image isdetermined. Thus (7+6+5+4+3+2+1)*n/8=7*n differences are calculated. Theaverage of the absolute values of these differences is then calculatedto give an objective measure of the symmetry of diamond 20.

[0094] In alternative embodiments of the present invention a measure ofthe fire of diamond 20 may be calculated by using an algorithm similarto that for determining scintillation. However, instead of measuring thedifference in light intensity levels, the difference in the relativeproportions of colour components (ie red, green, and blue (RGB)) betweena pixel from a first image (captured at a first rotational position) andits corresponding pixel (at the same coordinate position) from a secondimage (captured at a second rotational position, one rotational stepafter the first rotational position) are determined. This is repeatedfor all pixels within the circumference of diamond 20 in the first andsecond images, and for all pairs of first and second images captured atrotational positions which are one rotational step apart. For each pixelpair, the number of times the absolute difference in the relativeproportions of any of the three colour components is greater than apredetermined threshold is counted for all pixels in the circumferenceand for all pairs of images which are one rotational step apart. Theratio of this number over the total number of pixel pairs gives anobjective measure of the fire of diamond 20.

[0095] It will be appreciated that, with different shapes and/orsymmetries of particular gemstone cut patterns, such as square, oval,pear, heart-shaped or irregular shapes, the algorithms used to determinethe periphery of the gemstone and the various measurements of opticalproperties, as described above, may be varied to take into account theshape and symmetry of the particular gemstone cut pattern.

[0096] It will be appreciated that, with different shapes and/orsymmetries of particular gemstone cut patterns, such as square, oval,pear, heart-shaped or irregular shapes, the configuration of relativelyreflective regions 40 and relatively unreflective regions of concavesurface 26, may be varied to take into account the shape and symmetry ofthe particular gemstone cut pattern. It will also be appreciated thatthe configuration of relatively reflective regions 40 and relativelyunreflective regions of concave surface 26 may be varied to take intoaccount a particular property being determined. For instance, whendetermining a measure of the fire of a gemstone, it is desirable to forrelatively reflective regions 40 to be thin radial lines arranged aroundthe axis 22, such that the light pattern reflected comprises relativelynarrow peaks and relatively wide troughs. Thus, spectrally colouredlight will be generally less overpowered by white light and morevisible.

[0097] It will be appreciated that in alternative embodiments, concavesurface 26 may be held stationary within the apparatus and the platformis rotated instead. In this arrangement, the images captured of diamond20 rotate and extra processing is required to take that into accountwhen analysing those images. When comparing a first image at a firstrotational position with a second image at a second different rotationalposition (and with subsequent third, fourth . . . images) processingmust be performed so that pixels of the first and second (andsubsequent) images correspond to the same region or regions of diamond20. To achieve this, the second (and subsequent) image may be digitallyrotated back about the point corresponding to the centre of rotation ofthe platform to correct for the rotation of diamond 20 in the images.Alternatively, when comparing selected pixels of a first and second (orsubsequent) image, to obtain a measure of scintillation for example, thepixels of the second (or subsequent) image may be selected so as tocorrespond to a portion of the image rotated back about the pointcorresponding to the centre of rotation of the platform to correct forthe rotation of diamond 20. However, due to limitations on theresolution of the captured images, accuracy of comparison is reduced inboth cases and this arrangement is less preferable than the formerarrangement in which the platform is stationary and concave surface 26rotated.

[0098] It will be appreciated that in further alternative embodiments,concave surface 26 may be held stationary within the apparatus, andinstead the camera 30 and the platform both rotated by a single orseparate stepper motors in a coordinated fashion. This arrangementeliminates the need for extra processing to correct for the rotation ofthe images of diamond 20, but involves additional mechanical complexityand increased cost of manufacture.

[0099] While the above embodiment has described an apparatus arranged toi) support a gemstone having an axis of symmetry such that the axis ofsymmetry is parallel to the axis 22, ii) rotate the light patternrelative to the platform about the axis 22, and iii) capture images ofthe gemstone along the axis 22, it is important to realise that thepresent invention is not limited to this particular arrangement of thethree axes, although this arrangement is generally preferred. Inparticular, the axis of relative rotation between the light pattern andthe platform need not be co-linear or even parallel to the axis 22 (iefrom the axis parallel to an axis of symmetry of a gemstone whensupported in the apparatus) and/or the axis along which the images arecaptured need not be co-linear or even parallel to the axis 22.Furthermore, the axis of relative rotation between the light pattern andthe platform and the axis along which the images are captured need notbe co-linear or even parallel between themselves.

[0100] What is important is that a gemstone having an axis of symmetrymay be supported in the apparatus such that the axis of symmetry, theaxis of relative rotation between the light pattern and the means ofsupport, and the axis along which the images are captured arecoordinated such that i) the apparatus is able to take advantage of theshape and/or symmetry of the cut pattern of the particular gemstone whenrotating the light pattern relative to the gemstone, and ii) theapparatus is able to capture images of the gemstone, such as images ofthe crown of a SRB cut diamond, from which features resulting from theshape and/or symmetry of the gemstone may be observed. For instance, theaxis of relative rotation between the light pattern and the means ofsupport may be at an angle of incidence to the axis of symmetry of up toabout 30° without serious degradation to the performance of theapparatus. Similarly, the axis along which the images are captured mayat an angle of incidence to the axis of symmetry of up to about 45°without serious degradation to the performance of the apparatus.

1. An apparatus for generating data for use in determining a property ofa gemstone, such as a cut diamond, the apparatus comprising: a supportstructure for supporting a gemstone placed at an observation position,the support structure being arranged such that, if the gemstone has anaxis of symmetry, the gemstone is supportable such that the axis ofsymmetry is parallel to an axis X passing through the observationposition; illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern; rotation means arranged to causerelative rotation between the light pattern and the support structuregenerally about the axis X; a camera arranged to capture, at each of aplurality of rotational positions, an image of light returned by thegemstone and to output said images as image data.
 2. An apparatusaccording to claim 1, wherein the light pattern comprises at least onerelatively light region and at least one relatively dark region.
 3. Anapparatus according to claim 2, wherein the regions are arrangedradially generally about the axis X.
 4. An apparatus according to claim2 or 3, wherein the light pattern is generally symmetrical about theaxis X.
 5. An apparatus according to claim 4, wherein the light patternhas an n-fold symmetry, where n is a whole number multiple or factor ofs, a standardised gemstone cut having an s-fold symmetry.
 6. Anapparatus according to claim 5, wherein the light pattern has a 4-foldor 8-fold symmetry.
 7. An apparatus according to any preceding claim,wherein the illumination means comprises a reflector having a concavesurface arranged to reflect light generally towards the gemstone.
 8. Anapparatus according to claim 7, wherein the concave surface has at leastone relatively reflective region and at least one relativelyunreflective region, thereby creating said light pattern.
 9. Anapparatus according to claim 7 or 8, wherein the reflector is rotatablymounted in said apparatus generally about the axis X, thereby enablingrelative rotation between the light pattern and the support structuregenerally about the axis X.
 10. An apparatus according to any of claims7 to 9, wherein the illumination means comprises an annular light sourcearranged to emit light towards the concave surface and an annular bafflearranged to prevent direct light reaching the gemstone.
 11. An apparatusaccording to any preceding claim, wherein the support structure isrotatably mounted in said apparatus generally about the axis X, therebyenabling relative rotation between the light pattern and the supportstructure generally about the axis X.
 12. An apparatus according to anypreceding claim, comprising a data processing device arranged todetermine a property of the gemstone by comparing, using image datacorresponding to one or more of said electronic images, the intensity oflight at a first and a second image portion, each portion comprising oneor more pixels, said first and second image portions corresponding to afirst and a second region of the gemstone respectively, said first andsecond regions being related to each other in accordance with asymmetrical property of a standardised gemstone cut.
 13. An apparatusaccording to any preceding claim, comprising a data processing devicearranged to determine a property of the gemstone by comparing, usingimage data corresponding to two of said electronic images, the intensityof light at one or more pixels of a first image, captured at a firstrotational position, with the intensity of light at one or more pixelsof a second image, captured at a second rotational position different tosaid first rotational position, said one or more pixels of the firstimage corresponding to the same region or regions of the gemstone assaid one or more pixels of the second image.
 14. An apparatus accordingto any preceding claim, comprising a data processing device arranged todetermine a property of the gemstone by comparing, using image datacorresponding to two of said electronic images, the proportions ofcolour components at one or more pixels of a first image, captured at afirst rotational position, with the proportions of colour components atone or more pixels of a second image, captured at a second rotationalposition different to said first rotational position, said one or morepixels of the first image corresponding to the same region or regions ofthe gemstone as said one or more pixels of the second image.
 15. Amethod of using an apparatus according to any preceding claim.
 16. Anmethod of generating data for use in determining a property of agemstone, such as a cut diamond, the method comprising: supporting agemstone at an observation position, such that, if the gemstone has anaxis of symmetry, the gemstone is supportable such that the axis ofsymmetry is parallel to an axis X passing through the observationposition; illuminating the gemstone with a spatially varied lightpattern; causing relative rotation between the light pattern and thegemstone generally about the axis X; capturing, at each of a pluralityof rotational positions, an image of light returned by the gemstone. 17.A method of determining a property of a gemstone by comparing, usingimage data corresponding to one or more electronic images of thegemstone, the intensity of light at a first and a second image portion,each portion comprising one or more pixels, said first and second imageportions corresponding to a first and a second region of the gemstonerespectively, said first and second regions being related to each otherin accordance with a symmetrical property of a standardised gemstonecut.
 18. A method of determining a property of a gemstone by comparing,using image data corresponding to two or more electronic images of thegemstone captured under different lighting conditions, the intensity oflight at one or more pixels of a first image, captured under a firstlighting condition, with the intensity of light at one or more pixels ofa second image, captured under second different lighting condition, saidone or more pixels of the first image corresponding to the same regionor regions of the gemstone as said one or more pixels of the secondimage.
 19. A method of determining a property of the gemstone bycomparing, using image data corresponding to two or more electronicimages of the gemstone captured under different lighting conditions, theproportions of colour components at one or more pixels of a first image,captured under a first lighting condition, with the proportions ofcolour components at one or more pixels of a second image, capturedunder a second different lighting condition, said one or more pixels ofthe first image corresponding to the same region or regions of thegemstone as said one or more pixels of the second image.
 20. A computerprogram for performing the method of any of claims 17 to
 19. 21. Acomputer-implemented method of comparing properties of gemstones, suchas cut diamonds, the method comprising: receiving first image data inrespect of a first gemstone and second image data in respect of a secondgemstone, said first and second image data each comprising one or moreimages of said first and second gemstones, respectively; determining aproperty of each of said first and second gemstones in dependence onsaid first and second image data respectively; and simultaneouslydisplaying one or more images of each of said first and second gemstonestogether with a representation of the determined property for each ofsaid first and second gemstones.
 22. A computer program for performingthe method of claim
 21. 23. An apparatus for comparing properties ofgemstones, such as cut diamonds, the apparatus comprising: a supportstructure for supporting a gemstone placed at an observation position;illumination means arranged to illuminate a gemstone so placed; a cameraarranged to capture an image of light returned by a gemstone and tooutput said images as image data; and a data processing device arrangedto: receive first image data in respect of a first gemstone and secondimage data in respect of a second gemstone, said first and second imagedata each comprising one or more images of said first and secondgemstones, respectively; determine a property of each of said first andsecond gemstones in dependence on said first and second image datarespectively; and simultaneously display one or more images of each ofsaid first and second gemstones together with a representation of thedetermined property for each of said first and second gemstones.
 24. Anapparatus for generating data for use in determining a property of agemstone, such as a cut diamond, the apparatus comprising: a supportstructure for supporting a gemstone placed at an observation position,the support structure being arranged such that, if the gemstone has anaxis of symmetry, the gemstone is supportable such that the axis ofsymmetry is parallel to an axis X passing through the observationposition; illumination means arranged to illuminate a gemstone so placedwith a spatially varied light pattern; rotation means arranged to causerelative rotation between the light pattern and the support structure; acamera arranged to capture, at each of a plurality of rotationalpositions, an image of light returned by the gemstone generally alongthe axis X and to output said images as image data.
 25. An apparatus forgenerating data for use in determining a property of a gemstone, such asa cut diamond, the apparatus comprising: a support structure forsupporting a gemstone placed at an observation position; illuminationmeans arranged to illuminate a gemstone so placed with a spatiallyvaried light pattern; rotation means arranged to cause relative rotationbetween the light pattern and the support structure generally about anaxis X passing through the observation position; a camera arranged tocapture, at each of a plurality of rotational positions, an electronicimage of light returned by the gemstone generally along the axis X andto output said images as image data.
 26. An apparatus for generatingdata for use in determining a property of a gemstone, such as a cutdiamond, the apparatus comprising: a support structure for supporting agemstone placed at an observation position; illumination means arrangedto illuminate a gemstone so placed with a spatially varied lightpattern; rotation means arranged to cause relative rotation between thelight pattern and the support structure generally about an axis Xpassing through the observation position; a camera arranged to capture,at each of a plurality of rotational positions, an electronic image oflight returned by the gemstone and to output said images as image data.